What color is the car? You will probably want to apply a coat of sealant (lasts 3-6 months) and then top it with a coat of wax (lasts 3-8 weeks depending on the wax). This will give you good overall protection.

How long a sealant or wax will last is totally dependant upon how often the car is washed and/or maintained. If the car is typically washed 3-4 times per month then ANY sealant you apply to the car's paint will last 2-3 months before it needs to be reapplied. A good carnauba wax will give some protection atop the sealant but not much. The wax typically needs to be applied every 3-5 weeks to be effective as a protectant.

Jetseal 109 would be a good, fairly inexpensive sealant to use. I would even recommend a couple of coats be applied after the car's surface has been properly prepped ...... clayed at the very least. Jetseal will require some cure time between coats so plan to devote the better part of a weekend to the process. Any quality carnauba will work well to bring out the lustre of the paint ........ 50/50 Concours is also fairly inexpensive and works well with the Jetseal 109 product. Both can be had from Detailed Image .....

Poorboy's Natty's Blue is always a good choice for Jet Black. Great wax for a very reasonable price. Dodo Juice Blue Velvet or Purple Haze, as well as Dodo Juice Supernatural are all extremely good as well (albeit, a bit more expensive).

As ToadHollow said, you'll really want a sealant for long term protection though. Wax can be placed on top of a sealant for extra protection and depth/gloss/wetness to the paint.